In this talk, we focus on the discovery process of Web Services (WSs) by basing the search on the similarities among the service requirements, in order to cope with over-constrained queries or to find satisfactory alternatives for user requirements. This discovery process needs to involve the so-called Soft Constraint Satisfaction Problems (SCSPs). First we represent both WSs and the search query of the user as Rooted Trees, i.e., a particular form of Conceptual Graphs. Then, we find a homomorphism between these two trees as a solution of an SCSP. The main contribution is the enhanced expressiveness offered by this softness: in over-constrained scenarios, when a user query cannot be satisfied, classical crisp constraints (i.e., CSP) are not expressive enough to find close solutions to meet the users needs.